makes pointer(integer) from integer(pointer) without a cast

Question

#include<stdio.h>
#include<stdlib.h>

int **transpose(int a[], int b[], int raw, int column){
    int i, j;
    for(i=0; i < raw ; i++)
        for(j=0; j < column ; j++)
            *(b+(j*raw + i)) = *(a+(i*column + j));
    return *b;
}

int **mk_matrix(int raw, int col){
    int i;
    int **matrix = (int**)malloc(sizeof(int*)*raw);
    matrix[0] = (int*)malloc(sizeof(int)*(raw*col));
    for(i=1 ; i < raw ; i++)
        matrix[i] = matrix[i-1] + col;
    
    return matrix;
}

void main(void){
    int r, c, i, j;
    
    printf("Input the size of matrix : ");
    scanf("%d %d", &r, &c);
    
    int **matrix = mk_matrix(r, c);
    int **trans_matrix = mk_matrix(c, r);
    
    printf("Input elements of the %dx%d matrix : ", r, c);
    for(i=0; i < r ; i++)
        for(j=0; j < c ; j++)
            scanf("%d", &matrix[i][j]);
    
    **trans_matrix = transpose(matrix[0], trans_matrix[0], r, c);
    
    for(i=0; i < c ; i++){
        for(j=0; j < r ; j++)
            printf("%d ", trans_matrix[i][j]);
        printf("\n");
    }
}

In dev c++, this code runs correctly by I wanted but it comes

return makes pointer from integer without a cast -> return *b;
assignment makes integer from pointer without a cast -> **trans_matrix = transpose(matrix[0], trans_matrix[0], r, c); warnings.

How can i fix my code not showing warnings?

You are working in a StandAlone Environment on a microcontroller? If not, for starters C11 Standard - §5.1.2.2.1 Program startup(p1) applies. See also: What should main() return in C and C++?. Additionally, b is already a pointer to int. C11 Standard - 6.3.2.1 Other Operands - Lvalues, arrays, and function designators(p3) so attempting to return *b attempts to return type int. — David C. Rankin
– David C. Rankin, Commented Oct 5, 2020 at 3:54
wen compiling, always enable the warning, then fix those warnings. ( for gcc, at a minimum use: -Wall -Wextra -Wconversion -pedantic -std=gnu11 ) Note: other compilers use different options to produce the same results. Passing the OPs code through the compiler results in 4 major warnings. You need to fix those warnings, As it is, the results of the compile is NOT what you want. — user3629249
– user3629249, Commented Oct 5, 2020 at 22:10
OT: regarding: void main(void){ per the C standard, there are only 2 valid signatures for main(). They are: int main( void ) and int main( int argc, char *argv[]) — user3629249
– user3629249, Commented Oct 5, 2020 at 22:13

sachco · Accepted Answer · 2020-10-05 03:54:24Z

3

Well you don't need to

return *b

int **transpose(int a[], int b[], int raw, int column)

just modify above to

void transpose(int a[], int b[], int raw, int column){
    int i, j;
    for(i=0; i < raw ; i++)
        for(j=0; j < column ; j++)
            *(b+(j*raw + i)) = *(a+(i*column + j));
}

and in main function

**trans_matrix = transpose(matrix[0], trans_matrix[0], r, c);

to

transpose(matrix[0], trans_matrix[0], r, c);

as transpose function is already performing necessary changes to trans_matrix. You do not need to return.

this will resolve warning issue.

answered Oct 5, 2020 at 3:54

sachco

2942 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Shubham · Accepted Answer · 2020-10-06 08:19:09Z

In the function transpose() you are returning a ptr to int when the return type of transpose() is ptr to ptr to int. Now because you are returning the value of the wrong (not expected) data type, you are getting your second warning.

Another thing is when you are working with addresses of the matrices in the transpose() function you don't need to return any kind of value because ultimately you are changing values that are stored on that address. You are not working on a copy of that value. That's why you don't need to:

**trans_matrix = transpose(matrix[0], trans_matrix[0], r, c);

I don't know why you are overcomplicating the functions. You can write them as:

int transpose(int **a, int **b, int row, int column)
{
    int i, j;
    for(i=0; i < column ; i++)
        for(j=0; j < row ; j++)
            b[i][j] = a[j][i];
    return 0;
}

and

int **mk_matrix(int row, int col)
{
    int i;
    int **matrix = malloc(sizeof(int*)*row);

    for(i=0; i<row; i++)
        matrix[i] = malloc(sizeof(int)*(col));

    return matrix;
}

and in main() you just need to modify how you call the transpose() method:

transpose(matrix, trans_matrix, r, c);

P.S. Also, check if the memory space you are requesting(malloc()) is allocated to the ptr or not.

Collectives™ on Stack Overflow

makes pointer(integer) from integer(pointer) without a cast

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related